Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 55-56). / The water spider, a unique member of its species, is used as inspiration for a bubble capture mechanism. Bubble mechanics are studied in the pursuit of a biomimetic solution for transporting air bubbles underwater. Careful experimentation is performed to understand the mechanics of bubble formation and capture. Investigation of bubble formation through an underwater nozzle shows that bubble volume increases by 15% when parallel rods are spaced above the nozzle at the same width as the inner diameter of the nozzle. Bubble volume decreases linearly with increasing air injection rate. Decreasing surface tension by approximately 40% decreases bubble volume by approximately 20%. Changing the angle the nozzle from parallel to perpendicular with the bottom of the tank increases bubble volume 40%. Based on trends observed in the nozzle experiments and using the spider's mechanisms for bubble capture as inspiration, a bubble capture device is manufactured. Decreasing the surface tension of the fluid by 25% decreases captured bubble volume by 50%. Below a device submersion speed of approximately 2.4 mm/s, bubble formation was at a maximum for the device, regardless of fluid surface tension. This research elucidates the limitations on bubble capture by the water spider. For future applications, these limitations can be pinpointed and adjusted for more efficient bubble capture and plastron maintenance. / by Alice Brooks. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 89-90). / The performance of many electronic devices is presently limited by heat dissipation rates. One potential solution lies in high-performance air-cooled heat exchangers like PHUMP, the multiple condenser loop heat pipe presented here. This device features a number of design improvements that lead to significant increases in performance relative to state of the art heat exchangers. In this work, a compensation chamber is developed and implemented to ensure the operational stability of the device across a wide range of operating conditions. A computational model of the device was developed using COMSOL Multiphysics v3.5a to allow for design optimization and performance evaluation. The accuracy of this computational model was established by comparing simulation results to experimental data. Analytical models were used to identify operating points of interest, which were simulated to compare the performance of various designs. The final design featured reduced thermal resistance between the vapor in the evaporator and the compensation chamber, and increased thermal resistance between the compensation chamber and the ambient air relative to past designs. This design reduced the risk of condenser flooding and evaporator dry out, improving the operational stability of the device. This design was implemented into a ten-condenser prototype, where experiments validated its performance. The compensation chamber did not require any electrical heaters, reducing the power consumption of the device and increasing its COP. Finally, general recommendations and guidelines are presented for use during the design process of future compensation chambers. / by Nicholas Albert Roche. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002. / MIT Institute Archives copy bound: p. 1-78, 81-82, 79-80, 83-101. / Vita. / Includes bibliographical references (p. 81-84). / by Laura L. Proctor. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (p. 217-220). / by Paul Thomas Konkola. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 161-173). / In engineering practice, sheet metal often fails after complex strain paths that deviate substantially from the widely studied proportional loading paths. Different from previous works on the ductile fracture of sheet metal, this thesis research addresses the experimental and modeling issues related to the crack initiation in advanced high strength steels after loading direction reversal. The main outcome of the present work is a fracture initiation model for proportional and non-proportional loading. The starting point of this thesis is a first chapter on the development of a micromechanically-motivated ductile fracture initiation model for metals for proportional loading. Its formulation is based on the assumption that the onset of fracture is imminent with the formation of a primary or secondary band of localization. Motivated by the results from a thorough unit cell analysis, it is assumed that fracture initiates after proportional loading if the linear combination of the Hosford equivalent stress and the normal stress acting on the plane of maximum shear reaches a critical value. A comprehensive fracture initiation model is then obtained after transforming the localization criterion from the stress space to the space of equivalent plastic strain, stress triaxiality and Lode angle parameter using the material's isotropic hardening law. Experimental results are presented for three different advanced high strength steels. For each material, the onset of fracture is characterized for five distinct stress states, including butterfly shear, notched tension, tension with a central hole, and punch experiments. The comparison of model predictions with the experimental results demonstrates that the proposed Hosford-Coulomb model can predict with satisfactory accuracy the instant of ductile fracture initiation in advanced high strength steels. In a subsequent chapter, experimental methods are developed to perform compression tension experiments. In addition, a finite strain constitutive model is proposed combining a Swift-Voce isotropic hardening law with two Frederick-Armstrong kinematic hardening rules and a Yoshida-Uemori type of hardening stagnation approach. The plasticity model parameters are identified from uniaxial tension-compression stress-strain curve measurements and finite element simulations of compression-tension experiments on notched specimens. The model predictions are validated through comparison with experimentally-measured load-displacement curves up to the onset of fracture, local surface strain measurements and longitudinal thickness profiles. The extracted loading paths to fracture show a significant increase in ductility as a function of the compressive pre-strain. The Hosford-Coulomb model is therefore integrated into a non-linear damage indicator modeling framework to provide a phenomenological description of the experimental results for monotonic and reverse loading. Another extension of the modeling framework is presented in a third chapter inspired by the results from loss of ellipticity analysis. It is demonstrated that the Hosford-Coulomb model can also be expressed in terms of a stress-state dependent critical hardening rate. Moreover, it is shown that the critical hardening rate approach provides accurate predictions of the instant of fracture initiation for both proportional and non-proportional loading conditions. Enhancements of the finite strain constitutive model are also proposed to enable a fast identification of all model parameters. The plasticity model parameters are identified from stress-strain curve measurements from shear loading reversal on specimens with a uniform thickness reduced gage section. The model is used to estimate the local strain and stress fields in fracture experiments after shear reversal. The extracted loading paths to fracture show a significant increase in ductility as a function of the strain at shear reversal, a feature that is readily predicted by the prosed critical hardening rate model. / by Stephane Marcadet. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1994. / Includes bibliographical references (leaves 53-58). / by Steven A. Cimaszewski. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999. / Includes bibliographical references (p. 225-228). / by Edward Ramsey Snow. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000. / Includes bibliographical references (p. 119-127). / by Chee-Ming Chew. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1947. / Includes bibliographical references (leaves 50-51). / by Robert Stanley Sproule. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 29-30). / The need for specialized diesel fuel injectors is growing with increased efficiency and emissions regulation. These specialized fuel injectors have nozzle diameters of 150-200[mu]m which are susceptible to clogging from deposit formation. This thesis studies the deposit formation mechanisms with a thin fuel film reactor, and examines the potential for use of the reactor as a detergent screening tool. Through experimentation with the thin fuel film reactor it was found that temperature had negligible effect on the weight of a fully dried fuel film. This suggests that testing could be conducted at high or low temperatures to decrease the cycle time or increase test resolution respectively. It was also determined that dry deposits remain soluble in hot fuel immediately following drying, but become insoluble after long hot soak periods. A simple deposit formation model was constructed based on hypothesized formation factors. Although very simplified, the model matched the experimental results well. The correlation suggest that the hypothesized formation factors are critical to the formation process. The model should be expanded to explain deposit formation more generally, and further research should be conducted to better validate the model. / by Orian Welling. / S.B.